What does the waterfall model in SDLC assume about the phases of development?

The waterfall model in the Software Development Life Cycle (SDLC) operates on the premise that software development should occur in distinct phases that are completed in a linear, sequential order. This means that one phase must be fully finished before moving on to the next, without any overlap between them.

This structured approach helps ensure that each phase, such as requirements gathering, design, implementation, testing, and maintenance, is thoroughly completed before progressing. The model is built on the assumption that once a phase is complete, the development team will not return to it, which simplifies the management process and provides clear milestones for the project's progression. By adhering to this clear sequential flow, it aims to minimize risks associated with changes during the development process, allowing for better control and predictability of outcomes.

In contrast, the other options suggest ways of working that do not align with the waterfall model's foundational principles. For example, overlapping phases or completing phases in a non-sequential manner would create complexities that the waterfall model deliberately tries to avoid, as it can lead to confusion and project delays.